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Storm Windows: Impact Resistant Windows

Basics of Impact Resistant Windows


Impact Window
Courtesy of James Bowe

Impact Resistant Windows

Impact resistant windows or storm proof windows are composed of impact resistant glass, containing a layer of polyvinyl butaryl (PVB) between two slabs of glass. The most effective type of impact resistant window is the inner-membrane window. An impact resistant glass will probably shatter on impact but it will remain attached to the inner membrane along with the window frame. There is always the alternative of using a shatter resistant film that covers window glass, that will prevent glass from shattering.

Impact Resistant Windows Advantages

Impact resistant windows are being manufactures with polyvinyl membrane in the middle layer capable to withstand storm winds up to 200 miles per hour. These windows could also provide energy efficiency to your structure, including minimum sound disturbance and UV protection.

Some of the greater benefits of impact resistant windows are:

  • Come in different styles and sizes
  • Provide permanent protection against tornados, storms and hurricane at any time
  • Its high strength prevents the glass from breaking up into large sharp pieces
  • When glass cracks will create a ‘spider-like’ cracking pattern
  • A much higher sound insulation rating due to its damping effect
  • Blocks 99% of transmitted UV light
  • Some insurance companies could offer up to 45% premium discounts

Impact Resistant Windows Disadvantages

Impact resistant windows could also be costly and sometimes unaffordable. Adding an average of $65 per square foot, impact resistant windows could add a couple of thousands more to your construction project, but will eventually reduce your insurance costs. Shatter resistant film could be used as an alternative, but it less effective and could possibly fail under extreme wind conditions. Much of the noise reduction properties of laminated glass come from the air space between two panes of the laminate, not from the vinyl layer itself. If the windows are installed without the benefit of these air spaces, then the noise reduction properties are greatly reduced.

Impact Resistant Windows Facts

  • Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered
  • Impact resistant windows main design characteristics are the shatter-resistant glass securely fastened to a heavy duty aluminum frame
  • Hurricane windows are available in a variety of color tints, where blue is typically much more expensive
  • The Energy Conservation Code requires that impact resistant windows must comply with maximum U-factor of 0.75 or less and Solar Heat Gain Coefficient (SHGC) between 0.30 or less
  • Dampen unwanted outside sounds
  • Impact resistant windows have advanced to the point where they are thoroughly tested to withstand Category 5 wind conditions
  • The American Society for Testing & Materials (ASTM) has strict guidelines ( E1886 and E1996) for impact resistant windows before it can be certified as impact resistant.
  • Determine your site's ‘basic wind speed’ as found in the wind speed zone map from ASCE 7
  • · In all states, contractors should always check with local authorities to see if and how the provisions apply in their jurisdiction.

Impact Resistant Glass Types

The four major impact resistant glass types are identified by the laminate procedure or the window interlayer procedure:

  1. PVB –Polyvinyl Butyral – It is the most widely used product in the impact glass market since it does great when impacted and absorbs the impact.
  2. PVB with a layer of PET- It is a very tough product but its manufacturing process is quite challenging
  3. Sentry Glass Plus - More expensive than PVB and is normally used in some federal construction or specialized areas requiring bullet and bomb resistance glass.
  4. Resin Laminates- A liquid is poured between two glass layers and allowed to cure. For the manufacturer it is cheap, it is easy, and it is an acceptable.
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